1. Field of the Invention
Embodiments relate to a method and a device for controlling the movement of two transport units of a long-stator linear motor comprising a plurality n of long-stator linear motor (LLM) coils arranged adjacently in the direction of movement, the first transport unit comprising a first plurality of first drive magnets arranged adjacently in the direction of movement, and the second transport unit comprising a second plurality of second drive magnets arranged adjacently in the direction of movement, the movement of the first transport unit being controlled by an associated first transport controller in that the first transport controller calculates the electrical variables to be specified for a first portion of the plurality n of LLM coils, the movement of the second transport unit being controlled by an associated second transport controller in that the second transport controller calculates the electrical variables to be specified for a second portion of the plurality n of LLM coils, and it being checked whether a first controlled variable is specified by the first transport controller for an LLM coil as an electrical variable and whether a second controlled variable is specified by the second transport controller for said LLM coil as an electrical variable, and a long-stator linear motor comprising a device of this kind.
2. Discussion of Background Information
In a long-stator linear motor (LLM), a plurality of adjacent electrical LLM coils, which form the stator, are arranged adjacently so as to be fixed along a transport route. A number of drive magnets, either as permanent magnets or as an electrical coil or a short-circuit winding, is arranged on a transport unit, which magnets interact with the LLM coils. The long-stator linear motor may be designed as a synchronous machine, either self-excited or separately excited, or as an asynchronous machine. Due to the interaction of the (electro)magnetic fields of the drive magnets and the LLM coils, a propelling force acts on the transport unit and moves the transport unit forwards in the direction of movement. This occurs by actuating the individual LLM coils in order to control the magnetic flow. The magnitude of the propelling force is therefore influenced and the transport unit can be moved along the transport route in any desired manner. In this case, it is also possible to arrange a plurality of transport units along the transport route, the movements of which transport units can be controlled individually and independently of one another, in that the drive coils interacting with a transport unit can be energized respectively. Usually, an electrical variable is specified by a transport controller, which variable applies a terminal voltage to the coil terminals either directly or via a coil controller connected downstream or impresses a coil current into the LLM coil. Long-stator linear motors are characterized in particular by better and more flexible use over the entire operating range (rotational frequency, position, speed, acceleration), individual regulation/control of the movable transport units (shuttles), improved use of energy, a reduction of the maintenance costs due to the lower number of parts subject to wear, simple replacement of the transport means, efficient monitoring and error detection and optimization of the product flow. Long-stator linear motors are increasingly used as an alternative to conventional continuous conveyors or rotary-to-linear translation units (e.g. rotary motors on conveyor belt, drive belts, chains etc.) in order to satisfy the requirements of modern, flexible logistics units. Examples of long-stator linear motors of this kind can be found in WO 2013/143783 A1, U.S. Pat. No. 6,876,107 B2, US 2013/0074724 A1 or WO 2004/103792 A1.
In order to move a transport unit along the stator, a moved magnet field is generated along the stator by the LLM coils, as mentioned, which magnet field interacts with the drive magnets of the transport units. For this purpose, terminal voltages or coil currents of the LLM coils are controlled by a transport controller or a coil controller arranged downstream. In order to actuate the LLM coils or the coil controllers of the LLM coils, a transport controller for each transport unit is usually used, which transport controller, analogously to the rotary case, controls the currents and voltages to be applied to the individual LLM coils, proceeding from a d/q coordinate system. A transport unit therefore moves along the LLM coils of a stator, a transport controller actuating the adjacent LLM coils of the stator to a certain extent by means of an electromagnetic field.
However, if two transport units moved along the stator have different speeds, said units may approach one another. For example, a first transport unit may be stationary and another transport unit may move towards the first transport unit, or two transport units have opposite directions. In order to avoid a collision of the transport units, a safety measure is usually provided for preventing this.
US 2017/0117829 A1 concerns actuating the coil currents of LLM coils, copper losses being minimized. This takes into consideration that the LLM coils of a long-stator linear motor are influenced by the drive magnets of the transport units, too. Coil units consist of a group of coils. As is known, the total amount of the drive magnets of a transport unit must be greater than the individual actuable LLM coils of the stator, as the transport unit could not be moved otherwise. The second embodiment also concerns a case in which two transport units overlap a coil unit. The coil current of the central LLM coil of this coil unit is set to zero. However, this “absent” current is compensated by the additional LLM coils of the coil unit. In the third embodiment, a coil current applied to the coil unit is calculated if a transport unit is controlled only by one coil unit, i.e. overlaps the coils of the relevant coil unit.